Diagnosis of Microbeam Broadening From a Prototype Nanotechnology Microbeam Radiation Therapy Device Using Gafchromic EBT2 Film

Purpose:Most commercial dosimeters are not suitable for microbeam radiation therapy (MRT) due to the extremely small (<500μm) nature of the dose profiles inherent to this technique. This not only inhibits accurate dosimetry, but also hinders troubleshooting during the design of MRT devices. The aim of this work is to display that these problems can be overcome by using Gafchromic EBT2 film analyzed with FilmQA Pro.

Methods:Using Gafchromic EBT2 film and single-channel dosimetry, microbeam widening (by 20-30%) was observed during the long exposures necessary for delivering treatments to live mice, but was unobservable during short exposures. FilmQA Pro was used to analyze both short and long exposures with triple-channel dosimetry to further explore this problem. In addition, a multiple exposure was taken in which the beam was left on for two hours and the film was shifted every ten minutes to display how microbeam shape changed with tube on-time.

Results:Films that simply displayed microbeam broadening when analyzed with single-channel dosimetry appeared to show signs of having multiple peaks when analyzed with triple-channel dosimetry. This effect was more pronounced for long exposures than short exposures, but clearly visible in both cases when analyzed with triple-channel dosimetry. In the multiple exposure, the microbeam was shown to be moving as the on-time increased. Total movement matched what had previously been observed as a 50% increase in beam size in the most severe cases.

Conclusion:Gafchromic EBT2 film, when analyzed by triple-channel dosimetry, is not only capable of precisely reproducing microbeam peak doses, but is also capable of resolving tiny defects in the beam profile. This has allowed us to more completely characterize our microbeam device, optimize its use to create the cleanest dose profile possible, and preempt these problems in the design of our second generation device.